Wave signaling system



Dec. 19, 1933. w. A. STEEL WAVE SIGNALING SYSTEM Filed April 9, 1930 k D m. w

Z M Re on 4m m@ 1T E o WW w .IA ,n W A NYM Patented Dec. 19, 1933 UNITED STATES PATENT OFFICE 1,940,153 WAVE sIGNALiNG 'SYSTEM William Arthur Steel, Ottawa, Ontario, Canada '8 Claims.

This invention relates primarily to radio telegraph systems, particularly to the receiving portion of such systems.

A primary object of the invention is to provide 6 a radio telegraph receiving system wherein static,

atmospheric, or other undesirable electrical disturbances impinging upon the antenna are balanced out, minimized and substantially prevented from alecting the signal indicating device,

i, w whereas the desired signaling currents are segregated with high selectivity for suitable operation of the signal indicating element.`

A further object is to provide a radio telegraph system of the type specified wherein the coml ponents of the disturbing currents which are not completely balanced out and thus eliminated are nevertheless prevented from entering the circuit containing the signal indicating device, whereby the signals therein are at all times clear and dism tinct being unmasked by the disturbing effects.

The system ischaracterized in that it requires for signaling purposes the transmission of but a single frequency unmodulated carrier wave or a. carrier wave modulated at but a single audio 26 frequency.

Due to the balanced arrangement `of the circuit elements, the present invention may be readily adapted to the simultaneous reception of two different sets of signals operating on the same car- 30 rier frequency but modulated at slightly different audio-frequencies.

Other features of the system disclosed herein which are deemed novel to the present invention will appear more fully from thesubsequent descriptiOn.

It `is quite a general characteristic of radio receiving sets including-those intended for the reception of telegraph signals, that static or other atmospheric 'disturbances .as well as those aris- 40 ing from power sources, telephone or telegraph conductors andfother electrical circuits, tend to render reception of the desired signals diicult, if not impossible, due to the masking effect produced thereby upon the signal indicating device. This results from the fact that the disturbing currents are in the` absence of special precautions amplied along with the signaling currents and to the same degree within the limits of ,the amplifying equipment, as a consequence of which the relative effects produced upon the signal indicating device are in the same proportion as the relative magnitudes of the signal and dis` turbing currents owing in the antenna circuit.

The present invention relates to improvements in and additions to the radio receiver whereby the effects of the disturbing currents are Vbalanced out, while the signal current is selected, amplied and passed on to the signal indicator, where the effects produced are entirely free `from disturbances due to the undesired currents.

The invention is accomplished by connecting in sequence, an antenna circuit for picking up the signaling wave which also unavoidably picks up the undesired disturbing currents, a high-frequency amplifier which amplifies the sig-nal and disturbing currents to the same extent, a detector for rendering audible both. the signal and the disturbing currents, an audio-frequency ampliner for amplifying the frequencies within the audible range, and a divided circuit arrangement for eliminating the disturbing currents while selecting the signal.

'The divided circuit comprises two audio-frequency transformers having their primary windings connected in series to the audio-frequency ampliiier output, and having their respective secondary windings sharply tuned to slightly different audio-frequencies by means of suitable capacities in shunt therewith. Each tuned secondary winding is connected to the input of a threeelectrode thermionic device individual thereto operating as a current rectifier; the output circuits of the rectifier tubes being in lturn connected respectively to the opposite windings of a polarized relay, such for example, as the type known as B5 a British post oice relay.

The polar relay windings are ydifferentially connected in the respective vacuum tube output circuits as a result of which current supplied to the relay by one tube tends to operate the armature against one vContact while current supplied by the other tube tends to operate the armature against its opposite contact. Thus for equal currents simultaneously `supplied by the two Vtubes the resultant effect on the armature is nil. Preferably the polar relay is so adjusted that the armature is normally biased against one Contact, a. circuit to operate a signal indicating device being completed through the armature and the opposite or normally open contact of the relay.

The audio-frequency transformers referred to -are of special construction in that the secondary windings are of low resistance'and are tunable within the audio-frequency range preferably above 1000 cycles, inasmuch as the most serious disturbing currents are for the most part'of low audiofrequency. The secondary windings maybe such that the inherent capacity between turns is suflicient to tune them to approximately the desired audio-frequency. Or this result may be accomplished by connecting suitable fixed capacities in shunt therewith. Supplemental variable capacities are also connected in shunt with the transformer secondaries in order to adjust the tuning in each instance to exactly a desired frequency as explained below.

The respective transformer secondaries are tuned by kmeans of the variable capacities to slightly different audio-frequencies separated by' about 200 cycles, as for example 1000 and 1250 cycles. Due to the low resistances of the windings, the tuning is very sharp whereby a very high impedance is obtained at the resonant frequency which falls off at first rapidly and then more slowly for frequencies diverging by increasing amounts from the resonant frequency. Furthermore, owing to the slight difference in resonant frequencies of the two circuits, the resultant impedance-frequency curves substantially coalesce except for the regions in the immediate vicinity of the resonantlfrequences.

It results from this similarity in impedance frequency characteristics of the two transformer secondary circuits coupled with the fact that the primary windings are series connected to the de -tector output, that the disturbing currents, the more important of which after detection are as stated within the low audio-frequency range be low 1000 cycles, are impressed upon the rectifier tubes in substantially equal amounts at each instant whereby identical current effects are produced in their respective output circuits. And, inasmuch as the polar relay is differentially connected to the two output circuits, the resultant effect produced on the armature thereof is zero.

The series vconnection of the primary transformer windings ensures that the same instantaneous current will flow in each winding; while the similarity in impedance-frequency characteristics of the tuned circuits at other than the resonant frequencies causes equal instantaneous voltages due to the disturbing currents to be applied thereto. These instantaneous voltages in general, due to the fluctuating character of the disturbing currents, operate by shock excitation to set the tuned circuits into oscillation at their respective natural frequencies. Due to the slight difference in frequency of tuning for the two cir cuits, however, the resultant voltages impressed upon the tubes are substantially identical at each instant.

As regards the signal frequency,y however, which it is to be emphasized is of a sustained charm acter, the veffect produced is quite the reverse to that of the disturbing currents. Due to the sharp tuning of the resonant circuits, and to the fact that the impedances thereof decrease rapidly for slight frequency divergences on either side of the resonant frequencies, the signal frequency will produce a far greater effect upcn the vacuum tube having the input circuit tuned to that frequency than that produced upon the opposite tube. Thus the rectified signal currents flowing in the respective windings of the relay will differ in mag-1 nitude by an amount in general more than suffe cientto operate the armature against its normalM ly open contact for each pulse of signaling cur' rent received, the arrangement of the circuit elements being such as to insure this effect.

Having thus described'the principal features of the invention in general terms, reference will now be had'to the drawing fer a detailed eX- planation of aY specific embodiment thereof.

'In the drawing Figure 1 shows in circuit diagram forma 'complete radio telegraph receiving system in accordance with the present invention; while Figure 2 shows the manner of modifying the circuit of Figure 1 for the reception and automatic separation of two distinct sets of signals.

Referring to the drawing, A represents an antenna circuit tuned to the frequency of the incoming signal, and coupled by means of a transformer T to a radio-frequency amplifier B, the output of which is connected to a detector or demc-dulator circuit C which serves to convert the radio-frequency into audio-frequency currents. Connected to the detector output is an audio-frequency amplifier K.

The primary windings P1 and P2 of two special transformers T1 and T2 are connected in series to the output circuit of the audio-frequency amplifier K. The secondary windings S1 and S2 which are of low resistance are tuned by means of the fixed capacities C1 and C2 to approximately the desired frequencies for operation of the circuit. These capacities C1 and C2 mayv in whole or in part be physically distinct from the secondary transformer windings, or they may constitute the resultant of the natural capacities inherent between turns of the windings. The variable capacities K1 and K2 serve to accurately tune the secondaries S1 and S2 to audio-frequencies f1 and f2 in general differing in frequency by about 200 cycles. The tuned circuit constituting elements S1, C1 and K1, is designated as D1, while that constituting elements S2, C2 and K2 is designated D2.

The circuits D1 and D2 are connected between grid 1 and cathode 2 of thermionic tubes V1 and V2 respectively, which tubes are adapted by means ofthe common grid biasing battery 4 to operate as'rectifier tubes. The cathodes 2 are heated from the .common battery 5, the currents being individually adjustable by means of the separate rheostats 6. f

Transformer T1 is connected in reversed fashion relative to transformer T2 in order that the instantaneous voltages induced in tuned circuits D1 and D2 due to currents in the detector output will be impressed in the same sense between grid and filament of tubes V1 and V2 respectively.

The plate electrodes 3 of the tubes V1 and V2 are connected respectively through the windings E1 and E2 of the polarized relay E,Y and thence in common through the source ofV space-current supply 7 to the positive terminal of battery 5. The connections to the polarized relay windings are such that equal currents in the plate circuits of tubes V1 and V2 produce balancing effects upon the relay armature F so that no operating effect is produced. The armature F is normally biased against its spacing contact S for maintaining a signal'indicating circuit H open at the marking contact M of relay E.

The signal indicating device H in the present instance comprises battery 8 having one terminal connected to armature F and the other terminal connected in series through variable resistance 9, choke coils 10, and capacity 11 to the marking contact M. A pair of headphones P -are`connected across the terminals of capacity 11,

through the make-and-break contacts 13 of a buzzer 14, the buzzer being continuously vibrated by energization of its windings from battery 15 through make-and-break contacts 16 during closure of switch 17.

Although the buzzer 14 operates continuously to open and close contacts 13, nothing is heard in headphones P so long as the circuit of battery 8 is open at the markingl contact M of relay F.

When, however, the circuit through the marking contact M is closed, battery 8 charges condenser 1l during each interval that the buzzer ntacts 13.` are open. During the remaining intervals, i. e. while contacts 13 are closed, condfmser 11 discharges through telephones P, the circuit constants being such that the discharge is of an oscillatory character adapted to produce a clear and suitable tone in the headset.

The operation of the system as a whole is as follows: 'Die signaling as well as the undesired disturbing currents impinging upon the antenna circuit A are amplified in B, detected in C, and further amplified in K at audio frequency to a degree necessary to satisfactorily operate relay E. The modulated disturbing currents due to the substantially similar impedance characteristics of' tuned circuits D1 and VD1 at other than the resonant frequencies cause substantially equal voltages to be impressed upon the input circuits of tubes V1 and V2, whereby equal rectified currents flow in opposition through windings E1 and En respectively of relay E to produceV balancing effects on the amature F so that the operative position thereof' is not disturbed.

The modulated signaling current, however, which is of frequency f2 corresponding to the tuning of circuit D2, causes a maximum voltage to be impressed upon the input circuit of tube Vn, but a much smaller voltage upon the input to tube V1 due to the difference in frequency of tuning of the elements D1 and D2 coupled with the sharp tuning characteristics thereof. In this instance, therefore, a much larger rectified current flows through winding E: than through winding E1 'whereby amature F is operated against its marking contact M so long as a sustained signal is being received. During the interval that the relay is thus actuated against its marking contact a clear tone, produced in the manner explained above, is heard in the headphones P.

It was stated that the armature F of relay E normally rests against its spacing contact'S. This may be accomplished in a number of ways as, for example, by permanently biasing the relay either mechanically or magnetically; or by normally transmitting a carrier wave continuously from the sending station modulated by a frequency f1 corresponding to the tuning of circuit D1 to `actuate relay E against its spacing contact, the carrier wave during transmission of a marking signal being modulated by 'a different frequency fz corresponding to the tuning of circuit D2 to operate relay E' against its marking contact.

Or again, by operation of switch L, a source of frequency f may be impressed upon the detector C to heterodyne'an unmodulated steadily received signal frequency to a frequency f1 for normally holding relay E against its spacing contact, the signal frequency being changed slightly at the transmitting station during keying to produce a heterodyne frequency fz for operating the polar relay against the marking contact. Il' desirable, the autodyne method of reception may be resorted to wherein the detector C oscillates con` tinuously to supply the modulating frequency f1 in which case of course theseparate heterodyne source may be omitted Or still again, if the polar relay is mechanically or magnetically biased to spacing, the heterodyne or autodyne frequency f may act upon a single frequency unmodulated signal wave transmittedy in accordance with signals to produce a modulated current of frequency f2 for operating the polar relay E to marking corresponding to the signals received.

Figure 2 shows a portion of the circuit of Figure l as modified for the reception and diiierentiation of two different sets of signals differing slightly in frequency simultaneously received from two different transmitting stations or possibly from a single station adapted to transmit in this fashion. Conductors 18, 19 and 20 correspond to the like numbered conductors of Figure l, the complete receiving system for the circuit of Figure 2 being identical with that of the circuit of Figure 1 except for the portion shown.

Referring to Figure 2, the. polar relay E is provided with two independently operable armatures F1 and F2. Each of armatures F1 and F: is pivoted to operate between a pair of associated contacts S and M, individual thereto. ContactsS are, in eachv instance, so arranged that a preponderance of rectified signaling current flowing in winding E1 tends to operate both armatures against their respective contacts M. Contacts M, on the other hand, are so arranged that a preponderance of rectified signaling current flowing in winding E2 tends to operate both armatures against their respective contacts S. Armature F1 is normally biased mechanically, magnetically or otherwise, against its contact M, whereas armature F2 is similarly normally biasedv against its contact S. Armature F1 controls a circuit H1, similar to circuit H of Figure l for actuating headphones P1 in accordance with received signals. Armature F2 likewise controls a circuit H2 to actuate headphones Pz.

Assume now that two sets of signals differing slightly in frequency are simultaneously being received, one set of signals comprising a carrier wave modulated at frequency f1 corresponding to the tuning of resonant circuit D1, while the other set comprises a carrier wave modulated at frequency f2 corresponding to the tuning of resonant circuit D2.

'I'he signals of frequency f1 after being received and demodulated by detector C, are selected by resonant network D1 and substantially repressed by network D2 to produce a preponderance of recti'ed current in winding E1 of polar relay E which, as statedf'tends to operate both armatures F1 and F2 against their respective contacts M.

F2 Vagainst their respective contacts S. Armatures F2 being normally biased against its contact S, is not affected, whereas armature F1 being normally biased against its contact M is operated in accordance with the received signals of frequency fz.

It therefore results that with the circuit arrangement shown in Figure 2 signals of frequencies ,f1 and f2 simultaneously received are automatically differentiated in the circuit, the signals of frequency f1 being heard only in headphones P1, while signals of frequency f2 are heard only in the headphones Pz. The static or other interlio its

loll

fering currents are, of course, eliminated from both headphones P1 and P2, since such currents produce balancing effects on the armatures of the polar relay.

The single relay E of Figure 2 equipped with two armatures may, of course, be replaced by two relays each similar to that of Figure 1.

I claim:

l. A radio telegraph receiving system adapted to minimize the effects of static or other undesirable electrical disturbances comprising, means for receiving and detecting high-frequency disturbing and signaling currents to produce currents of audio-frequency, means for amplifying said currents of audio-frequency, a divided circuit comprising a pair of transformers having their primary windings serially connected to said amplifier output, the secondary winding of one said transformer being sharply tuned by capacitive means in shunt therewith to said signal frequency, the secondary winding of the other said transformer being similarly tuned by other capacitive means to a slightly different frequency, current rectifying means individual to said transformer secondaries, and signal indicating means differentially associated with the output sections of said rectifying means respectively, whereby the resulting disturbing currents are substantially balanced out and said signal current is rendered effective to operate said indicating means.

2. A radio telegraph receiving system adapted to minimize the effects of static or other undesirable electrical disturbances comprising, means for receiving and detecting high frequency disturbing and signal currents to produce currents of audio-frequency, means for amplifying said currents of audio-frequency, a divided circuit comprising a pair of audio-frequency transformers having their primary windings serially connected in opposition to said amplifier output, the secondary winding of one said transformer being sharply tuned by capacitive means in shunt therewith to said signal frequency, the secondary winding of the other said transformer being similarly tuned to a slightly different frequency, current rectifying means individual to said tuned transformer secondaries, a polar relay having its windings differentially connected in the output sections of said rectifying means respectively, whereby the resulting disturbing currents are substantially balanced out whereas the signal current isr rendered effective to operate said'relay, and signal indicating means controlled by said relay.

3. A radio telegraph receiving system as set forth in claim 2 wherein said signal indicating means comprises a condenser chargeable through an inductance from a potential source, an acoustical element connected across said condenser through contacts of an independently and continuously operable buzzer element, whereby said condenser is alternately charged and discharged in oscillatotry fashion through said acoustical element to produce a clear tone therein in accordance with said signal current. v

4. A radio telegraph receiving systemadapted to simultaneously receive two different sets of signals transmitted on the same carrier frequency but modulated at slightly different audio frequencies while minimizing the effects of static or other undesirable electrical disturbances comprising, means for receiving and detecting said signaling and disturbing currents to produce corresponding currents of` audio-frequency, means for vamplifying said currents of audio-frequency, a divided circuit connected to said amplier output, one portion of which is sharply tuned to one said signal frequency, the other portion being similarly sharply tuned to the rother said signal frequency, current rectifying means in each said portion, polarized relay means, a pair of independently operable armatures associated with the relay means, said relay means being differentially associated respectively with the output sections of said rectifying means whereby the effects of said disturbing currents are substantially balanced out whereas said signaling currents are rendered effective to operate said pair of armatures whereby one said armature responds to signals of one said frequency only and the other said armatureA responds to vsignals of the other said frequency only, and signal indicating means individual to and controlled by said rarmatures respectively.

5. A radio telegraph receiving system'adapted to receive a carrier Wave modulated in accordance with signals at a single audio-frequency and adapted further to minimize the effects of static or other undesirable electrical disturbances comprising, means for receiving, detecting and amplifying at audio-frequency said disturbing currents along with the signaling current, a divided circuit comprising a pair of audio-frequency transformers having their primary windings serially Vconnected in opposition to said amplifier output, and having secondary windings respectively of low resistance, the secondary winding of one said transformer being sharply tuned by capacitive means in shunt therewith to said signal frequency, the secondary winding ofthe other said transformer being similarly tuned to a slightly different frequency, current rectifying means individual to said tuned secondaries, a polar relay differentially connected in the output sections of said rectifying means respectively, whereby the resulting disturbing currents produce substantially balancing effects on said relay whereas the signal current is rendered effective to operate said relay, and signal indicating means controlled by said relay.

6. A radio telegraph receiving system adapted to receive unmodulated radio frequency signal currents of single frequency, and adapted further to minimize the effects of static or other undesirable electrical disturbances comprising,

ymeans for receiving disturbingl currents along with said signals, a local source of single frequency current and detecting means for rendering said signaling and disturbing currents audible, means for amplifying said currents of audiofrequency, a divided circuit comprising a pair of audio-frequency` transformers having their primary windings serially connected to said amplifier output, the secondarywinding of one said transformer being sharply tuned by capacitive means in shunt therewith to the signal frequency, the secondary winding of the other transformer being similarly tuned to a slightly different frequency, current rectifying means individual to said tuned transformer secondaries, a polar relay having its windings vdifferentially connected in the output sections of said rectifying means respectively. whereby the resulting disturbing currents produce substantially balancing effects on toreceive a carrier frequency modulated at two 'W' slightly separated audio-frequencies in accordance with marking and spacing signals, and adapted further to minimize the effects of static or other undesirable electrical disturbances comprising, means for receiving, detecting and amplifying at audio-frequency the disturbing currents along with the signaling currents, a divided circuit comprising a pair of audio freqency transformers having their primary windings serially connected to said amplifier output, the secondary windings being of low resistance, one said secondary sharply tuned by capacitive means in shunt therewith to the audio-frequency corresponding to said spacing signal, the other said secondary being similarly sharply tuned to the audio frequency corresponding to said marking signal, current rectifying means individual to said tuned transformer secondaries, a polar relay having its windings differentially connected in the output sections of said rectifying means respectively, whereby the resulting disturbing currents produce substantially balancing eiects upon said relay whereas said spacing signals are effective to operate said relay against one contact and said marking signals are effective to operate said relay against its other contact inV accordance with said signals.

8. A radio telegraph receiving system adapted to minimize the effects of static or other undesirable electrical disturbances comprising, means for receiving and detecting high-frequency disturbing and signaling currents to produce currents of audio-frequency, a divided circuit comprising a pair of transformers having their primary windings serially connected to said detector output, the secondary winding of one said transformer being sharply tuned by capacitive means in shunt therewith to said signal frequency, the secondary winding of the other transformer being similarly tuned by other capacitive means to a slightly different frequency, current rectifying means individual to said transformer secondaries, and signal indicating means differentially associated with the output sections of said rectifying means respectively, whereby the resulting disturbing currents are substantially balanced out and said signal current is rendered eiective to operate said indicating means.

WILLIAM ARTHUR STEEL. 

